Process of treating paper pulp



Patented July 31,1934

UNETED "STATES- PROCESS OF TREATING PAPER PULP Gotthard Rosen, Paris, France N Drawing. Application November 23, 1932, figilal No. 644,135. In France November 25,

13 Claims.

It is known that paper pulp' made from wood through the soda. or sulphate processes cannot be bleached, or at least cannot be bleached as easily as bisulphite paper pulp. Besides, if said pulps are bleached the resulting product is more or less yellowish. Up to the present time, the kraft pulp, which contains a considerable percentage of matters that are not baked or are only half baked, could not possibly be bleached.

In order to render that pulp capable of being bleached, it is therefore necessary to purify it so as to'diminish as far as possible the percentage of lignin, resin, incrustating bodies, etc., before subjecting the pulp to the bleaching treatment.

It is known that a treatment or even a supplementary heating of the pulpwith a rather concentrated soda lye is capable of efficaciously purifying the pulp. Thattreatment or that heating operation is however very expensive and they have the further disadvantage that the fibers are attacked, with a resulting considerable decrease of the yield and also a lower mechanical resistance. It has also been proposed to let the pulp remain for a certaintime in tanks or vats containing lime-milk, which is also capable of purifying the cellulose. However, such a method necessitates a very long treatment.

The object of my invention is to provide a process of treating paper pulp through which it is possible to transform the soda pulp or sulphate pulp into a pulp that can be easily bleached.

The process according to my invention consists essentially in subjecting the pulp successively to washing in a very diluted alkaline lye, washing in a very hot solution of an alkaline-earth base and chlorine water or soluble chlorides, and an acid treatment. The process according to my invention is very little expensive and can be applied for industrial purposes without necessitating any expensive supplementary plant.

After the residual lye has been eliminated from the pulp and after the ordinary washing, the pulp is subjected to a second washing in a very diluted alkaline lye (up to 1% NaOH, or NaOH mixed with NazCOs). That washing treatment may be performed at a temperature of 'about 80-90 C.

In some cases the temperature may be as high as 110 C. if the treatment is performed under a pressure of about 1 kilogram per square centimeter. After removing the lye, which may be utilized two or three times, the mass is first rinsed in ordinary water, and the pulp is subjected to a qthird washing in a hot solution of an alkaline .earth base and chlorine water or soluble chlorides (for instance up to 0.4% CaO and 0.4% NaCl).

A circulation of the liquid during the two washing operations above mentioned can eventually be provided. I Y

After removing the solution used for the thirdwashinghthe pulp is subjected to the ordinary 69 treatments until it reaches the refining piles.

A small quantity'of the lime and of the. salt is absorbed by the mass and remains therein during these ordinary treatments while the purifying of the cellulose is being carried on.

If the pulp is sufficiently well cooked, the sec ond washing, that is the washing with an alkaline lye, can be dispensed with- In that case, the third washing, that is the washing with av solution of an alkaline earth and of a salt, may be prolonged. 79

When the pulp has reached the piles, the mass is treated with a dilute solution of sulphuric acid (about 3 kilograms of sulphuric per 100kilograms of dry pulp). When the 'pulp has assumed a homogeneous colour, a solution of sodium chloride v is added (about 2 or 3 kilograms per 100 kilograms of dry pulp).

After that treatment, which lasts for a period of time ranging between half an hour and one hour, the pulp is washed with ordinary water. The pulp is then ready to bewashed through any of the known processes.

Through this treatment withsulphuric acid, the remainder of the lime iseliminated. At the same time a large proportion of the remaining hemi-cellulose is dissolved in the acid and is removed. The pulp then assumes a lighter colour.

The soda pulp or the sulphate pulp that has been thus treated can then be bleached as easily as bisulphite pulp.

In the case of the pulp being intended for the viscose artificial silk industry, for the nitro-cellulose industry, etc., it is highly. important-that the pulp should contain a minimum'of ashes. Now, through the treatment of the pulp with sulphuric acid, there is formed calcium sulphate, which is not soluble, and consequently cannot be eliminated through washing with water. The calcium sulphate is then precipitated onto the fibers and therefore causes an increase of the percentage of ashes in the pulp. In order to diminish that percentage, it'is therefore preferable to make use of an acid other than sulphuric acid for the last step of the process according to my invention. It is advantageous to choose an acid which gives with alkaline earth bases salts that are soluble in water, for instance hydrochloric acid, or even sulphurous acid in dilute solution.

In another mode of carrying out my invention,

the pulp may be subjected first to one of the washing treatments above referred to (very dilute alkaline solution, or hot solution of an alkaline earth base and of chlorine water or soluble chlorides), at a relatively low temperature, which may however be as high as '70-80 C., then to an acid treatment, for instance in sulphuric acid of very low concentration. The pulp thus treated is then subjected to a preliminary bleaching step with, for instance, from 1 to 2% of active chlorine. Said chlorine may be supplied by a solution of calcium chloride CaOClz or calcium hypochlorite (eau de Javel).

After that preliminary bleaching operation, the pulp is subjected to the other washing operation (hot solution of an alkaline earth base and chlorine water or soluble chlorides, or very dilute alkaline solution, as the case may be) and then to an acid treatment, for instance with hydrochloric acid tht is not very much concentrated.

After washing in ordinary water, the subsequent bleaching operation is performed in the known manner.

The process according to my invention is particularly well adapted for sulphate pulp or soda pulp, but it will readily be understood that it may be of very high interest for other paper pulps, for instance for bisulphite pulp.

What I claim is:

1. A method of treating paper pulp and particularly soda pulp and sulphate pulp, which comprises subjecting the pulp to a washing with a dilute solution of lye, to a washing with a hot solution of an alkaline earth base and of a chlorine containing water-soluble material of the group comprising chlorine and soluble chlorides, and to an acid treatment, whereby the pulp thus treated can be easily bleached.

2. A method of treating paper pulp and particularly soda pulp and sulphate pulp, which comprises subjecting the pulp to a washing with a dilute alkaline lye, to a washing with a hot solution of an alkaline-earth base and of a soluble chloride,,and to an acid treatment, whereby the pulp thus treated can be easily bleached.

3. A process of treating paper pulp and particularly soda pulp or sulphate pulp, which comprises subjecting the pulp to an ordinary washing, to a washing with a hot solution of an alkaline earth base in a liquid containing chlorine, and to an acid treatment, whereby the pulp thus treated can be easily bleached.

4. A process of treating paper pulp and particularly soda pulp or sulphate pulp, which comprises subjecting the pulp to an ordinary washing, to a washing with a dilute alkaline lye, to a washing with a hot solution of an alkaline earth base in a liquid containing chlorine, and to an acid treatment, whereby the pulp thus treated can be easily bleached.

5. A process of treating paper pulp and particularly soda pulp or sulphate pulp, which comprises subjecting the pulp to an ordinary washing, to a washing with a dilute alkaline lye, to a washing with a hot solution of an alkaline earth base in chlorine water, and to an acid treatment, whereby the pulp thus treated can be easily bleached.

6. A process of treating paper pulp and particularly soda pulp and sulphate pulp, which comprises subjecting the pulp to an ordinary washing, then to a washing with a dilute alkaline lye, to a washing with a hot solution of an alkaline earth base and a soluble chloride, and to an acid treatment, whereby the pulp thus treated can be easily bleached.

7. A process of treating paper pulp and particularly soda pulp and sulphate pulp, which comprises subjecting the pulp to an ordinary washing, then to a washing with a dilute alkaline lye, to a washing with a hot solution of an alkaline earth base in chlorine water, and to the action or sulphuric acid, whereby the pulp thus treated can be easily bleached.

8. A process of treating paper pulp and particularly soda pulp and sulphate pulp, which comprises subjecting the pulp to an ordinary washing, then to a Washing with a dilute alkaline lye, to a washing with a hot solution of an alkaline earth base in chlorine water, and to the action of hydrochloric acid, whereby the pulp thus treated can be easily bleached.

9. A process of treating paper pulp and particularly soda pulp and sulphate pulp, which comprises subjecting the pulp to an ordinary washing, then to a washing with a dilute alkaline lye, to a washing with a hot solution of an alkaline earth base in chlorine water, and to the action of sulphurous acid, whereby the pulp thus treated can be easily bleached.

10. A process of treating paper pulp and particularly soda pulp and sulphate pulp, which comprises, subjecting the pulp to an ordinary washing, then to a washing with a dilute alkaline lye, to a washing with a hot solution of an alkaline earth base and a soluble chloride, and to the action of sulphuric acid, whereby the pulp thus treated can be easily bleached.

11. A process of treating paper pulp and particularly soda pulp and sulphate pulp, which comprises, subjecting the pulp to an ordinary washing, to a washing with a dilute alkaline lye, to a washing with a hot solution of an alkaline earth base and of a soluble chloride, and to the action of hydrochloric acid, whereby the pulp thus treated can be easily bleached.

12. A process of treating paper pulp and particularly soda pulp andsulphate pulp, which comprises, subjeoting the pulp to an ordinary washing, to a washing with a dilute alkaline lye, to a washing with a hot solution of an alkaline earth base and of a soluble chloride, and to the action of sulphurous acid, whereby the pulp thus treated can be easily bleached.

13. A process of treating paper pulp and particularly soda pulp and sulphate pulp, which comprises, subjecting the pulp to a washing with a dilute alkaline lye at a temperature of less than subjecting to an acid treatment, and then to a preliminary treatment by means of chlorine, washing with a hot solution of an alkaline earth base in a liquid containing chlorine, and treating by an acid.

GOTTHARD ROSEN. 

